1. Field of the Invention
This invention relates to a filter element for the treatment of a fluid by the use of a reverse osmosis membrane, an ultrafilter membrane, a precision filter membrane, or a gas separation membrane as a separation membrane for various fluids which are used in various industries specializing in manufacture of electronic products, foodstuffs, beverages, medicines, fermentation Products, optical products, therapeutic products and precision products.
2. Description of the Prior Art
In the treatment of various fluids by the use of functional macromolecular membranes represented by the separation membranes mentioned above, the functional macromolecular membranes are generally required to be modular units. The separation membranes are formed into flat plates, tubes, hollow fibers, etc. and their modular units have their shapes determined by the shape of a relevant separation membrane.
The modules of flat plate type separation membranes are disclosed in JP-UM-B-55-49076 and JP-P-B-63-28654, for example. The former module is in such a shape as is obtained by punching a disc out of a flat plate type separation membrane and setting the disc directly in place on a holder and the latter module is in such a shape as is obtained by similarly punching a disc, joining the disc along the circumference thereof to a support, thereby forming a unit, and superposing a plurality of such units. JP-P-A-60-58208 also discloses a module which is in such a shape as is obtained by pleating a flat plate type separation membrane, joining the opposite edges of the membrane and converting the membrane into a tubular membrane, and closing the opposite open ends of the tubular membrane with a sealing material.
The modules using hollow fiber type separation membranes (hereinafter referred to as "modules of filter element") are disclosed in JP-UM-A-05-56227 and JP-P-A-06-170179, for example. They are in such a shape as is obtained by bundling a plurality of hollow fiber type separation membranes and closing one open end or both open ends of the bundle with a sealing material to create a watertight seal. The modules of filter element of this type are allowed to assume a large available membrane surface per unit volume of module because they do not require any support for membrane. Particularly, the inner surfaces of membrane are kept clean because the inner surfaces are not exposed to the open air. They also retain a high ability to clean the fluid under treatment by using the inner surfaces on the secondary side of fluid treatment. Further it is easy to manufacture cross flow type modules.
The modules of filter element possess various features besides those mentioned above as compared with the modules using the flat plate type and the tubular type separation membranes. In the manufacture thereof, the primary sides and the secondary sides thereof, relative to the flow of the fluid under treatment, must be watertight to isolate mutually in the open end parts of the bundle. For this purpose, the gaps between the adjacent hollow fiber type separation membranes must be sealed infallibly. This sealing has been, heretofore, attained generally by potting the gaps with such a potting material as polyurethane or epoxy resin which exhibits high flowability and, when mixed with other resin, manifests a hardening reaction. When the fluid subjected to the filtration is a highly active chemical substance such as acid or alkali, alcohol, ketone, ester, aromatic hydrocarbon, or chlorine type solvent and when such physical or mechanical working conditions as temperature and pressure are harsh, however, the modules are susceptible to physical and chemical invasion. When the potting material is improperly selected or the bonding strength is weak, the sealed parts tend to sustain a crack or peal. The modules of filter element thus have the problem of limiting the range of application in terms of the kind of fluid subjected to the treatment and the condition of use because they are deficient in durability.
The modules of filter element proposed in JP-P-A-01-164405 and JP-P-A-01-281104 for the Purpose of solving the problem mentioned above are such that the sealed parts are formed of a thermoplastic resin which is either identical to or compatible with the material for the hollow fiber type separation membranes. In this case, however, the hollow fiber type separation membranes in the sealed parts are thermally deteriorated or deprived of porosity to the extent of ultimate loss flexibility. To be specific, while the watertight contact between the hollow fiber type separation membranes and the sealed parts gains in thoroughness, the parts of the hollow fiber type separation membranes which are embedded in the sealed parts are embrittled to a point where they will be liable to succumb to chemical and physical invasion, hence sustain a crack. Further, the sealed parts in the conventional modules have no room for absorbing expansion or contraction, hence they have the problem of sustaining a crack in the sealed parts themselves or in the hollow fiber type separation membranes.
This invention has been developed as a result of numerous diligent studies pursued with a view to overcoming the problems suffered by the prior art as described above. The object of this invention is to provide a filter element which is possessed of high durability to resist various chemical and physical invasion.